Fix not applicable on ambigious ident pat for merge_match_arms

Example
---
```rust
enum X {
    A,
    B,
    C,
}
use X::*;
fn main() {
    match A {
        $0A => todo!(),
        B => todo!(),
        C => todo!(),
    }
}
```

**Before this PR**

Assist not applicable

**After this PR**

```rust
enum X {
    A,
    B,
    C,
}
use X::*;
fn main() {
    match A {
        A | B => todo!(),
        C => todo!(),
    }
}
```

Author: A4-Tacks

crates/ide-assists/src/handlers/merge_match_arms.rs

@@ -160,9 +160,14 @@ fn get_arm_types<'db>(
                     }
                 }
                 ast::Pat::IdentPat(ident_pat) => {
+                    let has_type = ctx.sema.type_of_pat(local_pat).is_some();
                     if let Some(name) = ident_pat.name() {
                         let pat_type = ctx.sema.type_of_binding_in_pat(ident_pat);
-                        map.insert(name.text().to_string(), pat_type);
+                        let is_local_variable = !has_type || pat_type.is_some();
+
+                        if is_local_variable {
+                            map.insert(name.text().to_string(), pat_type);
+                        }
                     }
                 }
                 _ => (),
@@ -212,6 +217,40 @@ fn main() {
         );
     }
 
+    #[test]
+    fn merge_match_arms_ambigious_ident_patterns() {
+        check_assist(
+            merge_match_arms,
+            r#"
+#[derive(Debug)]
+enum X { A, B, C }
+use X::*;
+
+fn main() {
+    let x = A;
+    let y = match x {
+        A => { 1i32$0 }
+        B => { 1i32 }
+        C => { 2i32 }
+    }
+}
+"#,
+            r#"
+#[derive(Debug)]
+enum X { A, B, C }
+use X::*;
+
+fn main() {
+    let x = A;
+    let y = match x {
+        A | B => { 1i32 },
+        C => { 2i32 }
+    }
+}
+"#,
+        );
+    }
+
     #[test]
     fn merge_match_arms_multiple_patterns() {
         check_assist(